Climate warming effect on peat accrual rate in modern time

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Peatland ecosystems have been accumulating substantial amounts of carbon (C) over centuries and millennia as a consequence of their decomposition rates being slower than organic matter production. As a result, it has been estimated that the current C stock at these ecosystems amounts to 273-547 Pg C. The current and predicted rise in global temperature is likely to affect northern ecosystems more than other ecosystems. Higher temperature can enhance decomposition with potentially large losses of C that is currently stored belowground, further exacerbating global warming. Yet, the potential consequences on peatland C accrual rates are for most part unknown. In this study we investigated, using trace isotopes (14C and 137Cs), recent rates of C accrual in three bogs located in Northern Minnesota. At all sites Sphagnum moss is the predominant understory vegetation and all systems have low pH and are nutrient poor. Bulk density appears to decline with increasing depth, while C% and N% are fairly constant, despite some variability. Across sites, Bog Lake showed significantly lower N%, not surprisingly considering that Bog Lake is the most nutrient-poor of all sites. Radiocarbon analyses of the extracted cellulose from the Sphagnum moss allowed identifying the spike in weapon testing-derived 14C, corresponding to the early 1960s (located at approximately 15-18 cm depth). 137Cs detections were less clear, possibly due to mobilization of the isotope at low pH. Preliminary data suggest that in recent times (corresponding to approximately the top 3 cm of peat) decomposition has been enhanced compared to past decades.